$ rails g model Foo title:string date:datetime
...
$ cat spec/support/blueprints.rb 
require 'machinist/active_record'

# Add your blueprints here.
#
# e.g.
#   Post.blueprint do
#     title { "Post #{sn}" }
#     body  { "Lorem ipsum..." }
#   end

Foo.blueprint do
  title { "MyString" }
  date { "2010-10-09 16:44:25" }
end